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Information furnished by Analog Devices is believed to be accurate andreliable. However, no responsibility is assumed by Analog Devices for itsuse, nor for any infringements of patents or other rights of third partieswhich may result from its use. No license is granted by implication orotherwise under any patent or patent rights of Analog Devices.

a Low Voltage, Resistor ProgrammableThermostatic SwitchAD22105

Analog Devices, Inc., 1996

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A

Tel: 617/329-4700 Fax: 617/326-8703

FEATURES

User-Programmable Temperature Setpoint2.0 C Setpoint Accuracy

4.0 C Preset Hysteresis

Wide Supply Range (+2.7 V dc to +7.0 V dc)

Wide Temperature Range (40 C to +150 C)

Low Power Dissipation (230 W @ 3.3 V)

APPLICATIONS

Industrial Process Control

Thermal Control Systems

CPU Monitoring (i.e., Pentium)

Computer Thermal Management Circuits

Fan Control

Handheld/Portable Electronic Equipment

The AD22105 is designed to operate on a single power supplyvoltage from +2.7 V to +7.0 V facilitating operation in batterypowered applications as well as in industrial control systems.Because of low power dissipation (230 W @ 3.3 V), self-heating errors are minimized and battery life is maximized.

An optional internal 200 k pull-up resistor is included tofacilitate driving light loads such as CMOS inputs.

Alternatively, a low power LED indicator may be driven directly

GENERAL DESCRIPTION

The AD22105 is a solid state thermostatic switch. Requiringonly one external programming resistor, the AD22105 can be setto switch accurately at any temperature in the wide operatingrange of 40C to +150C. Using a novel circuit architecture,the AD22105 asserts an open collector output when the ambienttemperature exceeds the user-programmed setpoint temperature.The AD22105 has approximately 4C of hysteresis which preventsrapid thermal on/off cycling.

FUNCTIONAL BLOCK DIAGRAM

1

2

3

4

8

7

6

5

NC

VS

RSET

NC

RPULLUP

OUT

GND

NC TEMPERATURESENSOR

200k

SETPOINT

AD22105

1 2 3 4

8 7 6 5

OUT

+2.7V TO +7.0V

RSETAD22105TOP VIEW

Figure 1. Typical Application Circuit

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AD22105SPECIFICATIONSParameter Symbol Conditions Min Typ Max Units

TEMPERATURE ACCURACYAmbient Setpoint Accuracy ACC 0.5 2.0 CTemperature Setpoint Accuracy ACCT 40C TA +125C 3.0 CPower Supply Rejection PSR +2.7 V1 < VS < +7.0 V 0.05 0.15 C/V

HYSTERESIS

Hysteresis Value HYS 4.1 C

OPEN COLLECTOR OUTPUTOutput Low Voltage VOL ISINK= 5 mA 250 400 mV

POWER SUPPLYSupply Range VS +2.7 +7.0 VSupply Current, Output LOW ISON 120 ASupply Current, Output HIGH ISOFF 90 A

INTERNAL PULL-UP RESISTOR RPULL-UP 140 200 260 k

TURN-ON SETTLING TIME tON 5 s

NOTES1The AD22105 will operate at voltages as low as +2.2 V.

Specifications subject to change without notice.

REV. 02

(VS = 3.3 V, TA = +25 C, RLOAD = internal 200 k, unless otherwise noted)

SET POINT TEMPERATURE C

80

0

70

40

30

20

10

60

50

5

15

25

35

45

55

65

75

50 15025

RSET-k

0 25 50 75 100 125

RSET = 90.3k39 MC

TSET (C) + 281.6 C

Figure 2. Setpoint Resistor Values

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AD22105

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ABSOLUTE MAXIMUM RATINGS*

Maximum Supply Voltage . . . . . . . . . . . . . . . . . . . . . . . +11 VMaximum Output Voltage (Pin 2) . . . . . . . . . . . . . . . . +11 VMaximum Output Current (Pin 2) . . . . . . . . . . . . . . . 10 mAOperating Temperature Range . . . . . . . . . . 50C to +150CDice Junction Temperature . . . . . . . . . . . . . . . . . . . . +160CStorage Temperature Range . . . . . . . . . . . . 65C to +160C

Lead Temperature (Soldering, 10 sec) . . . . . . . . . . . +300C*Stresses above those listed under Absolute Maximum Ratings may causepermanent damage to the device. This is a stress rating only and functional

operation of the device at these or any other conditions above those listed in theoperational sections of this specification is not implied. Exposure to absolutemaximum rating conditions for extended periods may affect device reliability.

ORDERING GUIDE

Package Package

Model Description Option

AD22105AR 8-Lead SOIC SO-8AD22105AR-REEL7 8-Lead SOIC SO-8

PIN CONFIGURATION

1

2

3

4

8

7

6

5

NC = NO CONNECT

AD22105

RPULL-UP

NC

RSET

VS

NC

OUT

GND

NC

TOP VIEW(Not to Scale)

PIN DESCRIPTION

Pin No. Description

1 RPULL-UP, Internal 200 k (Optional)

2 OUT

3 GND

4 No Connection

5 No Connection

6 RSET

, Temperature Setpoint Resistor

7 VS8 No Connection

WARNING!

ESD SENSITIVE DEVICE

CAUTION

ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily

accumulate on the human body and test equipment and can discharge without detection.

Although the AD22105 features proprietary ESD protection circuitry, permanent damage may

occur on devices subjected to high energy electrostatic discharges. Therefore, proper ESD

precautions are recommended to avoid performance degradation or loss of functionality.

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AD22105Typical Performance Characteristics

REV. 04

ERR

ORC

TEMPERATURE C

4

450 15025 0 25 50 75 100 125

3

0

1

2

3

2

1

GUARANTEED LIMIT (+)

GUARANTEED LIMIT ()

Figure 3. Error vs. Setpoint

ERROR

C/%

TEMPERATURE C

0.1

0.3

1.150 15025 0 25 50 75 100 125

0.5

0.7

0.9

Figure 4. Setpoint Error Due to RSETTolerance

ISA

TEMPERATURE C

90

4050 15025 0 25 50 75 100 125

80

60

50

70

VS = 7V

VS = 5V

VS = 3V

Figure 5. Supply Current vs. Temperature (VOUT= HIGH)

HYST

ERESIS

C

TEMPERATURE C

4.4

3.250 15025 0 25 50 75 100 125

4.2

4.0

3.8

3.6

3.4

Figure 6. Hysteresis vs. Setpoint

ERROR

C

VS

2.0

1.5

2.03 74 5 6

0.0

0.5

1.0

1.5

1.0

0.5

+125C

+25C

40C

Figure 7. Setpoint Error vs. Supply Voltage

ISA

TEMPERATURE C

120

6050 15025 0 25 50 75 100 125

110

100

90

80

70

VS = 7V

VS = 5V

VS = 3V

Figure 8. Supply Current vs. Temperature (VOUT = LOW)

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AD22105

REV. 0 5

0.4

0.3

0.010A 10mA1mA100A1A

0.2

0.1

IOUT

V

OUT

TA = +150C

TA = +25C

TA = 40C

Figure 9. VOUT vs. IOUT(VOUT = LOW)

sec

FLOW RATE CFM

16

14

20 1200400 800

10

8

6

4

12

Figure 10. Thermal Response vs. Flow Rate

FLOW RATE CFM

250

200

0 1200

JA

C/W

400 800

150

100

50

Figure 11. Thermal Resistance vs. Flow Rate

%OFFINALVALUE

TIME sec

100

80

00 6010 20 30 40 50

60

40

20

90

70

50

30

10

STILL AIR

MOVING AIR

(1200 CFM)

Figure 12. Thermal Response Time

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PRODUCT DESCRIPTION

The AD22105 is a single supply semiconductor thermostatswitch that utilizes a unique circuit architecture to realize thecombined functions of a temperature sensor, setpoint comparator,and output stage all in one integrated circuit. By using oneexternal resistor, the AD22105 can be programmed to switch atany temperature selected by the system designer in the range of

40C to +150C. The internal comparator is designed to switchvery accurately as the ambient temperature rises past thesetpoint temperature. When the ambient temperature falls, thecomparator relaxes its output at a somewhat lower temperaturethan that at which it originally switched. The difference betweenthe switch and unswitch temperatures, known as the hysteresis,is designed to be nominally 4C.

THE SETPOINT RESISTOR

The setpoint resistor is determined by the equation:

RSET =39 MC

TSET(C)+281.6C90.3k Eq. 1

The setpoint resistor should be connected directly between theRSET pin (Pin 6) and the GND pin (Pin 3). If a ground plane isused, the resistor may be connected directly to this plane at theclosest available point.

The setpoint resistor, RSET, can be of nearly any resistor type,but its initial tolerance and thermal drift will affect the accuracyof the programmed switching temperature. For most applications,a 1% metal-film resistor will provide the best tradeoff betweencost and accuracy. Calculations for computing an error budgetcan be found in the section Effect of Resistor Tolerance andThermal Drift on Setpoint Accuracy.

Once RSET has been calculated, it may be found that the calcu-lated value does not agree with readily available standard

resistors of the chosen tolerance. In order to achieve an RSETvalue as close as possible to the calculated value, a compoundresistor can be constructed by connecting two resistors in seriesor in parallel. To conserve cost, one moderately precise resistorand one lower precision resistor can be combined. If the mod-erately precise resistor provides most of the necessary resistance,the lower precision resistor can provide a fine adjustment. Con-sider an example where the closest standard 1% resistor has only90% of the value required for RSET. If a 5% series resistor isused for the remainder, then its tolerance only adds 5% of 10%or 0.5% additional error to the combination. Likewise, the 1%resistor only contributes 90% of 1% or 0.9% error to the combi-nation. These two contributions are additive resulting in a totalcompound resistor tolerance of 1.4%.

EFFECT OF RESISTOR TOLERANCE AND THERMAL

DRIFT ON SETPOINT ACCURACY

Figure 3 shows the typical accuracy error in setpoint temperatureas a function of the programmed setpoint temperature. Thiscurve assumes an ideal resistor for RSET. The graph of Figure 4may be used to calculate additionalsetpoint error as a functionof resistor tolerance. Note that this curve shows additional errorbeyond the initial accuracy error of the part and should be

added to the value found in the specifications table. For example,consider using the AD22105 programmed to switch at +125C.Figure 4 indicates that at +125C, the additional error isapproximately 0.2C/% of RSET. If a 1% resistor (of exactlycorrect nominal value) is chosen, then the additional error couldbe 0.2C/% 1% or 0.2C. If the closest standard resistorvalue is 0.6% away from the calculated value, then the total

error would be 0.6% for the nominal value and 1% for thetolerance or (1.006) (1.10) or 1.01606 (about 1.6%). Thiscould lead to an additional setpoint error as high as 0.32C.

For additional accuracy considerations, the thermal drift of thesetpoint resistor can be taken into account. For example, con-sider that the drift of the metal film resistor is 100 ppm/C.Since this drift is usually referred to +25C, the setpoint resistorcan be in error by an additional 100 ppm/C (125C 25C) or1%. Using a setpoint temperature of 125C as discussed above,this error source would add an additional 0.2C (for positive drift)making the overall setpoint error potentially 0.52C higher thanthe original accuracy error.

Initial tolerance and thermal drift effects of the setpoint resistor

can be combined and calculated by using the followingequation:

RMAX = RNOM(1+ ) 1+TC(TSET 25C)( )where:

RMAX is the worst case value that the setpoint resistor can be atTSET,

RNOM is the standard resistor with a value closest to the desiredRSET,

is the 25C tolerance of the chosen resistor (usually 1%,5%, or 10%),

TC is the temperature coefficient of the available resistor,

TSET is the desired setpoint temperature.

Once calculated, RMAX may be compared to the desired RSETfrom Equation 1. Continuing the example from above, therequired value of RSET at a TSET of 125C is 5.566 k. If thenearest standard resistor value is 5.600 k, then its worst casemaximum value at 125C could be 5.713 k. Again this is+2.6% higher than RSET leading to a total additional error of0.52C beyond that given by the specifications table.

THE HYSTERESIS AND SELF-HEATING

The actual value of the hysteresis generally has a minordependence on the programmed setpoint temperature as shownin Figure 6. Furthermore, the hysteresis can be affected by self-heating if the device is driving a heavy load. For example, if the

device is driving a load of 5 mA at an output voltage (given byFigure 9) of 250 mV, then the additional power dissipationwould be approximately 1.25 mW. With a JA of 190C/W infree air the internal die temperature could be 0.24C higherthan ambient leading to an increase of 0.24C in hysteresis. Inthe presence of a heat sink or turbulent environment, theadditional hysteresis will be less.

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AD22105

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OUTPUT SECTION

The output of the AD22105 is the collector of an NPN transistor.When the ambient temperature of the device exceeds theprogrammed setpoint temperature, this transistor is activatedcausing its collector to become a low impedance. A pull-upresistor, such as the internal 200 k provided, is needed toobserve a change in the output voltage. For versatility, the

optional pull-up resistor has notbeen permanently connectedto the output pin. Instead, this resistor is undedicated andconnects from Pin 7 (VS) to Pin 1 (RPULL-UP). In order to useRPULL-UP a single connection should be made from Pin 1(RPULL-UP) to Pin 2 (OUT).

The 200 k pull-up resistor can drive CMOS loads sinceessentially no static current is required at these inputs. Whendriving LS and other bipolar family logic inputs a parallelresistor may be necessary to supply the 20 A50 A IIH (HighLevel Input Current) specified for such devices. To determinethe current required, the appropriate manufacturers data sheetshould be consulted. When the output is switched, indicating anover temperature condition, the output is capable of pulling

down with 10 mA at a voltage of about 375 mV. This allows fora fan out of 2 with standard bipolar logic and 20 with LSfamily logic.

Low power indicator LEDs (up to 10 mA) can be drivendirectly from the output pin of the AD22105. In most cases asmall series resistor (usually of several hundred ohms) will berequired to limit the current to the LED and the outputtransistor of the AD22105.

MOUNTING CONSIDERATIONS

If the AD22105 is thermally attached and properly protected, itcan be used in any measuring situation where the maximumrange of temperatures encountered is between 40C and+150C. Because plastic IC packaging technology is employed,

excessive mechanical stress must be avoided when fastening thedevice with a clamp or screw-on heat tab. Thermally conductiveepoxy or glue is recommended for typical mounting conditions.In wet or corrosive environments, an electrically isolated metalor ceramic well should be used to protect the AD22105.

THERMAL ENVIRONMENT EFFECTS

The thermal environment in which the AD22105 is useddetermines two performance traits: the effect of self-heating onaccuracy and the response time of the sensor to rapid changes intemperature. In the first case, a rise in the IC junction tempera-ture above the ambient temperature is a function of two variables:the power consumption of the AD22105 and the thermalresistance between the chip and the ambient environment, JA.

Self-heating error can be derived by multiplying the powerdissipation by JA. Because errors of this type can vary widely forsurroundings with different heat sinking capacities, it isnecessary to specify JA under several conditions. Table I showshow the magnitude of self-heating error varies relative to theenvironment. A typical part will dissipate about 230 W atroom temperature with a 3.3 V supply and negligible outputloading. In still air, without a heat sink, Table I indicates aJA of 190C/W, which yields a temperature rise of 0.04C.Thermal rise of the die will be considerably less in an environ-ment of turbulent or constant moving air or if the device is indirect physical contact with a solid (or liquid) body.

Response of the AD22105 internal die temperature to abruptchanges in ambient temperatures can be modeled by a singletime constant exponential function. Figure 11 shows typicalresponse plots for moving and still air. The time constant, (time to reach 63.2% of the final value), is dependent on JA andthe thermal capacities of the chip and the package. Table I liststhe effective for moving and still air. Copper printed circuit

board connections were neglected in the analysis; however, theywill sink or conduct heat directly through the AD22105s solderplated copper leads. When faster response is required, a therm-ally conductive grease or glue between the AD22105 and thesurface temperature being measured should be used.

Table I. Thermal Resistance (SO-8)

Medium JA ( C/Watt) (sec)*

Moving Air** 100 3.5Without Heat Sink

Still Air 190 15Without Heat Sink

NOTES**The time constant is defined as the time to reach 63.2% of the final tempera-

ture change.**1200 CFM.

USING THE AD22105 AS A COOLING SETPOINT

DETECTOR

The AD22105 can be used to detect transitions from higher

temperatures to lower temperatures by programming thesetpoint temperature 4C greater than the desired trip pointtemperature. The 4C is necessary to compensate for thenominal hysteresis value designed into the device. A moreprecise value of the hysteresis can be obtained from Figure 6. Inthis mode, the logic state of the output will indicate a HIGH for

under temperature conditions. The total device error will beslightly greater than the specification value due to uncertainty inhysteresis.

APPLICATION HINTS

EMI Suppression

Noisy environments may couple electromagnetic energy into theRSET node causing the AD22105 to falsely trip or untrip. Noisesources, which typically come from fast rising edges, can becoupled into the device capacitively. Furthermore, if the outputsignal is brought close the RSET pin, energy can couple from theOUT pin to the RSET pin potentially causing oscillation. Straycapacitance can come from several places such as, IC sockets,multiconductor cables, and printed circuit board traces. In somecases, it can be corrected by constructing a Faraday shieldaround the RSET pin, for example, by using a shielded cable withthe shield grounded. However, for best performance, cablesshould be avoided and the AD22105 should be soldered directlyto a printed circuit board whenever possible. Figure 13 shows asample printed circuit board layout with low inter-pin capaci-tance and Faraday shielding. If stray capacitance is unavoidable,and interference or oscillation occurs, a low impedance capaci-tor should be connected from the RSET pin to the GND pin.This capacitor must be considerably larger than the estimatedstray capacitance. Typically several hundred picofarads will cor-rect the problem.

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AD22105

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Leakage at the RSET Pin

Leakage currents at the RSET pin, such as those generated from amoist environment or printed circuit board contamination, canhave an adverse effect on the programmed setpoint temperatureof the AD22105. Depending on its source, leakage current canflow into or out of the RSET pin. Consequently, the actualsetpoint temperature could be higher or lower than the intended

setpoint temperature by about 1C for each 75 nA of leakage.With a 5 V power supply, an isolation resistance of 100 Mwould create 50 nA of leakage current giving a setpointtemperature error of about 0.7C (the RSET pin is near groundpotential). A guard ring can be placed around the RSET node toprotect against leakage from the power supply pin (as shown inFigure 13).

C1

PIN 1

OUT

GND

VS

RSET

Figure 13. Suggested PCB Layout

OUTLINE DIMENSIONSDimensions shown in inches and (mm).

8-Lead SOIC

(SO-8)

0.1968 (5.00)

0.1890 (4.80)

8 5

41

0.2440 (6.20)

0.2284 (5.80)

PIN 1

0.1574 (4.00)

0.1497 (3.80)

0.0688 (1.75)

0.0532 (1.35)

SEATINGPLANE

0.0098 (0.25)

0.0040 (0.10)

0.0192 (0.49)

0.0138 (0.35)

0.0500(1.27)BSC

0.0098 (0.25)

0.0075 (0.19)

0.0500 (1.27)

0.0160 (0.41)

80

0.0196 (0.50)

0.0099 (0.25)x 45